Process for Making a Heat Exchanger

ABSTRACT

A process for making a heat exchanger comprising extruding a profile ( 1 ) composed of a number of parallel tubes ( 2 ) and web-like portions ( 3 ) interconnecting said tubes ( 2 ), removing part of the connection made by the web-like portions ( 3 ) and expanding the extruded product in a direction perpendicular to the longitudinal direction of the tubes ( 2 ) and providing connecting means for allowing a fluid to flow through said tubes.

The invention relates to a process for making a heat exchanger.

Heat exchangers are generally known in the art and one common typeconsists of a number of parallel tubes, fin-like elements being providedbetween each part of neighbouring tubes. An example of such a heatexchanger has been described in U.S. Pat. No. 5,780,825. Such heatexchangers can be either a so-called parallel flow heat exchanger, or asingle flow heat exchanger such as a serpentine like heat exchanger.

Normally such heat exchangers are produced by extruding a number oftubes, making a set of fins to be placed between each pair ofneighbouring tubes, and providing end connectors or collectors to theend portion of the tubes, where upon the whole assembly is brasedtogether.

It is an object of the invention to provide a process for making a heatexchanger, which is less complicated to make, and in which lesscomponents need to be handled in order to obtain the final assembly ofthe heat exchanger.

This and other objects are achieved in that a profile is extruded whichis composed of a number of parallel tubes and web-like portionsinterconnecting said tubes, in that part of the connection made by theweb-like portions is removed and the extruded product is expanded in adirection perpendicular to the longitudinal direction of the tubes, andin that connecting means are provided allowing a fluid to flow throughthe tubes.

In this way it is obtained that based upon a single extrusion a heatexchanger can be obtained which is as efficient as the standard heatexchanger, and which can be obtained with less efforts.

It must be remarked that it is well known that extruded aluminiumprofiles can be shaped and manipulated in order to produce mesh-shapedproducts. Such products have been described in GB-A-2 101176, AU-A 84 27721 and GB-A-1 588 197. In all these examples the ribs forming the meshhave been considered as being solid and the product is only envisaged ina mesh functionality.

In this type the products, the aluminium extrusions comprising solidribs lined by the webs in converted by cutting slots a specific lengthin the webs and thereafter stretching the profile laterally.

By using tubular elements in stead of solid elements and fin likeprotrusions it is possible to modify the heat transfer characteristics.By varying the length of the slots cut into the web part of the extrudedprofiles before stretching in a lateral manner, it is possible to affectthe air flow patterns and induce turbulence which will further improveheat transfers.

Other advantages and characteristics of the invention will become clearfrom the following description reference being made to the annexeddrawings, in which:

FIG. 1 is a perspective view of an extruded profile as seen in thedirection of the tubes, which can be used in the process according tothe invention,

FIG. 2 is a perspective view of the profile of FIG. 1,

FIG. 3 is a perspective view of the product obtained after expanding theprofile according to FIG. 1 and 2,

FIG. 4 is a perspective view corresponding to FIG. 1 of a modifiedprofile,

FIG. 5 is a perspective view corresponding to FIG. 2 of the modifiedprofile of FIG. 4,

FIG. 6 is a perspective view of the product obtained after expanding theprofile according to FIG. 4 and 5, and

FIG. 7 is a perspective view of a completed heat exchanger obtained bymeans of the profile according to FIG. 1 and 2.

In FIG. 1 and 2 there is shown a first profile 1 which can be used inthe process according to the invention. The profile 1 consists of anumber of parallel tubes 2 and a number of webs 3 interconnecting eachpair of neighbouring tubes 2. As shown all tubes are located in the sameplane and have a ring shaped cross-section, but it will be obvious thatit is not required to have all tubes 2 in the same plane and that anysuitable cross-section can be used, such as flat tubes, hexagonal tubes,etc . . . .

After extrusion of the profile, each web 3 is provided with a number ofslots 4, extending parallel to the tubes 2. In the embodiment shown theslots 4 have a length which is substantially longer than the remainingweb portion between two adjacent slots in the same web. Moreover theslots 4 in the different webs are all positioned in the same way withrespect to the end face of the extruded profile.

After expansion of the profile in a direction perpendicular to thelongitudinal direction of the tubes 2 a product as shown in FIG. 3 willbe obtained. The tubes 2 have been deformed so as to form curved tubesand between each part of adjacent tubes air gaps 8 originating from theslots 4 have been formed.

By providing suitable connecting means to the end portions of the tubes,so as to form an input and an output for a fluid and interconnecting thedifferent tubes a fluid heat exchanger can be obtained.

In FIG. 7 there is shown such a heat exchanger which in this case is asingle flow heat exchanger. However it will be obvious that by simplyreplacing the U-shape end connectors by a manifold type a parallel flowheat exchanger can be obtained.

In the FIGS. 4-6 there is shown a modified embodiment of an extrudedprofile 11. The profile 11 as extruded comprises a number of paralleltubes 12, each pair of neighbouring tubes 12 being connected by means ofa web 13. As shown all tubes 12 are in the same plane and have a ringshaped cross-section, but as explained with respect to the firstembodiment, other shapes are possible as well.

Each web 13 is provided with a number of protruding portions extendingfrom both faces of the web 13. In the embodiment shown there are fourprotruding portions 14, 15, 16, 17 having a planar shape, and theextrusions 14 and 15 are located in the same plane as the extrusions 16and 17 respectively.

It will be obvious that other types or shapes of protruding portions anddifferent numbers than four are possible.

After extrusions of the profiles 11, a number of slots is made in eachweb, as shown in FIG. 5. A first set of slots 18 is made in the web 13between each tube 11 and the protruding portions 14, 16 and 15,17respectively. All the slots 18 have the same length and the sameposition with respect to the end of the tube 12. Between the protrudingportions 14, 16 and 15, 17 another set of slots 19 is made. Basicallyeach slot 19 has the same length as the slot 18.

Their position however is such that as seen along the longitudinaldirection of the tubes 12 each slot 19 is extending halfway between twosuccessive slots 18 in the neighbouring part of the same web 13.

In this way each web 13 is provided with a number of slots 18, 19whereby the slots 19 are offset with respect to the slots 18.

After expansion of the extruded profile in the direction perpendicularto the axis of the tubes 12, a product as shown in FIG. 6 will beobtained, in which a fin-like construction 20 is present between eachpair of neighbouring tubes. Based upon the product as shown in FIG. 6 itis possible to make a heat exchanger as explained with respect to theFIG. 3.

In order to test the performance of a heat exchanger obtained by meansof the extruded and expanded products a test made with a heat exchangerof the type shown in FIG. 7.

EXAMPLE

A profile consisting of 8 tubular members 8 mm outside diameter with a1.0 mm wall thickness and an interconnecting web of 2 mm width similarto the profile shown in FIG. 1 was produced. Slots were made in the web,64 mm long and the profile was sideways stretched from an initialdimension of 78 mm wide to 128 mm wide. (i.e. 64% extension)

Individual expanded profiles were assembled to make a panel with overallwidth of 360 mm and a height of 300 mm. Tubes were interconnected bymeans of ‘U’ bends so that flow paths within each set of panels could becontrolled. The size of the panels was matched to the available openingon a wind tunnel that was used to assess the heat transfer efficiency ofthe system.

A conventional tube and fin brazed radiator, designed for automotiveuse, was used in the trials to provide comparative data to existingstate of art heat exchangers.

Oil, preheated to 100° C., was passed through the tubular profiles atrates of either 150 or 300 litres per hour and the wind speed was variedfrom 4 metres per second up to 11 metres per second. The temperature ofthe out-going oil was measured after an operating time of 5 minutes.

Efficiency was calculated using the formula

(T_(oil inlet)−T_(oil outlet))/(T_(oil inlet)−T_(Air.))

Where oil inlet is 100° C. and the air temperature is 20° C.

Thus, for a panel consisting of 3 layer with each layer being a separateoil circuit and where oil flow rate is 150 litres/hr and the wind speedis 11 m/sec, the temperature drop for oil is (100-49.6)° C. and thedifference between oil inlet and ambient air temperature is 80° C., anefficiency of 0.64 is calculated.

The results from the testing are detailed in table 1-6.

Best heat transfer results were obtained with oil flow of 150 litres perhour in the test panels as well as in the conventional radiator.Surprisingly, the extruded panel heat exchanger performed up to over 70%of the efficiency of the state of art heat exchanger. This is despitethe fact that the air-side flow path had not been optimised and theshape of the tubular elements was not optimised. Ideally the tubeprofile would preferably be oval or tear-drop shaped and couldincorporate internal fin to enhance heat transfer.

TABLE 1 3 layer 3 flow paths Oilflow 150 l/hr Oilflow 300 l/hr Windspeed 4 8 11 4 8 11 m/s OilTempOut 65.4 54.2 49.6 79.2 69.9 61.8 ° C.Performance 2521 3336 3681 3017 4094 4284 Watt Efficiency 0.44 0.57 0.640.26 0.37 0.43

TABLE 2 3 layer 6 flow paths Oilflow 150 l/hr Oilflow 300 l/hr Windspeed 4 8 11 4 8 11 m/s OilTempOut 67.5 58.2 53.9 80 72.8 68.3 ° C.Performance 2389 3051 3342 2909 3942 4337 Watt Efficiency 0.42 0.53 0.590.25 0.35 0.39

TABLE 3 2 layer 2 flow paths Oilflow 300 l/hr Oil Pressure Oilflow 150l/hr drop too high Wind speed 4 8 11 4 8 11 m/s OilTempOut 72.7 62.858.5 ° C. Performance 2030 2742 3038 Watt Efficiency 0.35 0.48 0.53

TABLE 4 2 layer 4 flow paths Oilflow 150 l/hr Oilflow 300 l/hr Windspeed 4 8 11 4 8 11 m/s OilTempOut 73.2 65 60.9 84.2 77.7 75.1 ° C.Performance 1965 2576 2850 2267 3137 3582 Watt Efficiency 0.34 0.45 0.50.2 0.28 0.32

TABLE 5 1 layer 6 flow paths Oilflow 150 l/hr Oilflow 300 l/hr Windspeed 4 8 11 4 8 11 m/s OilTempOut 84.7 80 77.4 91 88.2 86.3 ° C.Performance 1104 1456 1624 1199 1691 1926 Watt Efficiency 0.19 0.25 0.280.11 0.15 0.17

TABLE 6 Radiator - Benchmark Oilflow 150 l/hr Oilflow 300 l/hr Windspeed 4 8 11 4 8 11 m/s OilTempOut 39.9 32.0 31.0 59.2 52.8 50.4 ° C.Performance 4266 4566 5060 6134 6851 7183 Watt Efficiency 0.77 0.85 0.850.51 0.59 0.62

1. A process for making a heat exchanger comprising extruding a profilecomposed of a number of parallel tubes and web-like portionsinterconnecting said tubes, removing part of the connection made by theweb-like portions and expanding the extruded product in a directionperpendicular to the longitudinal direction of the tubes and providingconnecting means for allowing a fluid to flow through said tubes.
 2. Aprocess according to claim 1, characterized in that each web-likeportion forms a connection between two neighbouring tubes.
 3. A processaccording to claim 2, characterized in that the web-like portionconsists of a flat plate.
 4. A process according to claim 2,characterized in that the web-like portion comprises a flat plateforming the connection between the neighbouring tubes and fin-likeprotrusions provided under an angle on the surface of the flat plate. 5.A process according to claim 4, characterized in that on each face ofeach flat plate two parallel fin-like protrusions have been made.
 6. Aprocess according to claim 2, characterized in that the connection madeby each web-like portion is removed in such a way that in each web likeportion there is a number of openings and a number of connections whichare alternating, and in that the position of the openings is shifted towith respect to the openings in the neighbouring webs.
 7. A processaccording to claim 5, characterized in that the removal of the web isdone in such a way that the flat plate is partly interrupted in theportion between the tubes connected by the plate and the fin-likeprotrusion and the flat plate is partly interrupted between the twofin-like protrusions.
 8. A process according to claim 1, characterizedin that exchange is made as a parallel flow heat exchanger.
 9. A processaccording to claim 1, characterized in that the heat exchanger is madeas a serpentine flow heat exchanger.
 10. A process according to claim 2,characterized in that exchange is made as a parallel flow heatexchanger.
 11. A process according to claim 3, characterized in thatexchange is made as a parallel flow heat exchanger.
 12. A processaccording to claim 4, characterized in that exchange is made as aparallel flow heat exchanger.
 13. A process according to claim 5,characterized in that exchange is made as a parallel flow heatexchanger.
 14. A process according to claim 6, characterized in thatexchange is made as a parallel flow heat exchanger.
 15. A processaccording to claim 7, characterized in that exchange is made as aparallel flow heat exchanger.
 16. A process according to claim 2,characterized in that the heat exchanger is made as a serpentine flowheat exchanger.
 17. A process according to claim 3, characterized inthat the heat exchanger is made as a serpentine flow heat exchanger. 18.A process according to claim 4, characterized in that the heat exchangeris made as a serpentine flow heat exchanger.
 19. A process according toclaim 5, characterized in that the heat exchanger is made as aserpentine flow heat exchanger.
 20. A process according to claim 6,characterized in that the heat exchanger is made as a serpentine flowheat exchanger.
 21. A process according to claim 7, characterized inthat the heat exchanger is made as a serpentine flow heat exchanger.